A laser processing machine has been widely used that cuts a plate material formed of metal using a laser beam emitted from a laser oscillator. In the laser processing machine, various laser oscillators are used. In order to cut a plate material with a high speed having a relatively thin plate thickness, a fiber laser oscillator is frequently used, for example. The fiber laser oscillator not only has an advantage in that it is suitable for high-speed cutting of a plate material, but also has an advantage in that it has a smaller size and lower costs than a CO2 laser oscillator.